As the need for wireless devices increases, wireless UWB implementations are increasingly turned to meet this need. A UWB radio can provide a fast, low power transmission scheme. UWB signals generally have a continuous fractional bandwidth (i.e., the ratio of the −10 dB bandwidth to the center frequency) of at least 25%. However, a signal can fall outside of this basic range and still be considered “UWB.” For example, the Federal Communications Commission (FCC) refers to a signal in the 3.1 to 10.6 GHz range with a center frequency of 500 MHz as UWB. Thus, the above measurement is just a rough guideline.
However, UWB devices suffer several important limitations. One of the biggest of these limitations is the restrictions imposed on UWB transmissions by the FCC. In February of 2002, the FCC issued regulations regarding the use of UWB devices. These regulations imposed significant bandwidth and spectral power limits on any UWB transmissions. They also limited the bandwidth available for UWB transmission.
Another limitation in the United States is the presence of the UNII (Unlicensed National Information Infrastructure) band right in the middle of the frequency band allocated to UWB. The FCC has allocated the range of 3.1 GHz to 10.6 GHz for UWB, and the UNII band falls in the range of 5.15 to 5.85 GHz. The UNII band is used by unlicensed devices such as cordless phones and 802.11a wireless local area network (WLAN) devices. Because of the high power levels permitted devices in the UNII band (sometime up to one hundred times the power levels of UWB transmissions), it is preferable for UWB devices to avoid transmitting in those bands.
Although the UNII band is offered as an example of a frequency band that a UWB device may wish to avoid, in some embodiments it may be desirable to avoid other frequency bands.
Furthermore, as the circumstances change, these restrictions may be increased or decreased, reducing or expanding the bandwidth available for UWB transmissions.
In addition, although UWB devices in the United States must meet the restrictions imposed by the FCC and preferably avoid the UNII band, these parameters will not apply in other countries. And though no other country has as yet regulated UWB transmissions, it seems likely that they will impose power and bandwidth restrictions as the FCC has done in the United States. However, it seems equally likely that the specific parameters of these restrictions will not track exactly with the parameters of the restrictions imposed by the FCC.
Furthermore, other countries and regions are likely to have some equivalent to the UNII band, i.e., a band dedicated to cordless phones and WLANs, with varying locations and bandwidth in the available frequency spectrum. For example, the Japanese equivalent of the UNII band falls between 4.90 to 5.4 GHz. UWB devices operating in these regions may wish to avoid these frequency bands as well.
Therefore, it would be desirable to provide a UWB device that would be easily modified to broadcast using different bandwidths and different center frequencies. This would allow the device to account for changes in available spectrum over the course of time, and in different jurisdictions.
It would also be desirable to provide a device that uses all of the available UWB bandwidth, but still avoids certain sensitive bands located within that available bandwidth.